Near-Surface Disorder in Single-Crystal Silicon Carbide (4H-SiC) Induced by MeV Light Ion Irradiation

Author(s):

John Derek Demaree, Noel Guardala, Zois Tsinas, and Mohamad Al-Sheikhly

Abstract:

Single-crystal silicon carbide (4H-SiC) was irradiated with 1770 keV hydrogen (H) ions and 4300 keV helium (He) ions to investigate the nature of the damage that might be induced by exposure to protons, fast neutrons, or alpha particles in a nuclear reactor or waste storage environment. Raman spectroscopy and ion beam channeling were used to investigate the extent and nature of the disorder caused by light ion irradiation just under the surface of the material, rather than at the end of the ion beam range. The results suggest that the Monte Carlo simulation program SRIM correctly predicts the relative amount of ballistic displacement induced by H and He ions, as measured by the number of antisite defects and extinction of characteristic Raman features, with complete chemical disorder and elimination of important electronic properties achieved at less than 0.08 displacements per atom (dpa). In contrast, ion beam channeling measurements indicated that full structural disorder (amorphization) required much higher levels of atomic displacement. In the case of H irradiation, the rate of disorder accumulation was consistent with the direct-impact/defect-stimulated (DI/DS) model found in other studies, with no evidence of temperature-induced defect recombination. In the case of He irradiation, the overall amount of amorphization and loss of crystallinity was only 25% of that expected from the same low-temperature DI/DS model. These results are discussed in light of a possible ionizationinduced recrystallization or defect recombination mechanism induced not directly by the He ions, but by ionization in the cascades of the highest energy recoil atoms.